Sepsis is a major cause of morbidity and mortality in humans and other animals. In the United States, sepsis is the second leading cause of death in intensive care units among patients with non-traumatic illnesses. It is also the leading cause of death in young livestock, affecting 7.5-29% of neonatal calves, and is a common medical problem in neonatal foals. Despite the major advances of the past several decades in the treatment of serious infections, the incidence and mortality due to sepsis continues to rise.
Sepsis results from the systemic invasion of microorganisms into blood and can present two distinct problems. First, the growth of the microorganisms can directly damage tissues, organs, and vascular function. Second, toxic components of the microorganisms can lead to rapid systemic inflammatory responses that can quickly damage vital organs and lead to circulatory collapse (i.e., septic shock) and, often times, death.
Sepsis is a systemic reaction defined by the American College of Chest Physicians and the Society of Critical Care Medicine by a systemic inflammatory response (SIRS) in response to a confirmed infectious process. SIRS is defined by the presence of two or more of the following: altered body temperature (<36° C. or >38° C.), tachycardia (heart rate>90/min), tachypnea (respiratory rate>20/min) or hypocapnia (PaCO2 less than 4.3 kPa), leucopenia (white blood cells (WBCs)<4000 cells/mm3 or leucocytosis (>12000 WBC/mm3) or >10% band forms. The confirmation of the infectious process is confirmed by microbiological means (stain, culture, antigenemia or antigenuria, nucleic acid detection) or pathognomonic signs of infection obtained by imaging or clinical examination. The infection can affect any organ system, but the more severe cases present as septicemia (i.e., organisms, their metabolic end-products or toxins in the blood stream), bacteremia (i.e., bacteria in the blood), toxemia (i.e., toxins in the blood), endotoxemia (i.e., endotoxin in the blood). Sepsis can also result from fungemia (i.e., fungi in the blood), viremia (i.e., viruses or virus particles in the blood), and parasitemia (i.e., helminthic or protozoan parasites in the blood). Thus, septicemia and septic shock (acute circulatory failure resulting from septicemia often associated with multiple organ failure and a high mortality rate) may be caused by various microorganisms.
There are three major types of sepsis characterized by the type of infecting organism. For example, gram-negative sepsis is the most frequently isolated (with a case fatality rate of about 35%). The majority of these infections are caused by Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. Gram-positive pathogens such as the Staphylococci and Streptococci are the second major cause of sepsis. The third major group includes fungi, with fungal infections causing a relatively small percentage of sepsis cases, but with a high mortality rate; these types of infections also have a higher incidence in immunocomprised patients.
Some of these infections can be acquired in a hospital setting and can result from certain types of surgery (e.g., abdominal procedures), immune suppression due to cancer or transplantation therapy, immune deficiency diseases, and exposure through intravenous catheters. Sepsis is also commonly caused by trauma, difficult newborn deliveries, and intestinal torsion (especially in dogs and horses). Infections in the lungs (pneumonia), bladder and kidneys (urinary tract infections), skin (cellulitis), abdomen (such as appendicitis), bone (osteomyelitis) and joints (arthritis) and other areas (such as meningitis) can spread and also lead to sepsis. In some circumstances, ingestion of microbe-contaminated water, fluid or food, or contact with microbe-covered environmental surfaces can cause infections that lead to sepsis, and infection with food-borne and water-borne pathogens such as Shigella spp, or certain serotypes of Escherichichia coli (such as O157H7), Salmonella spp including Salmonella enterica serovar typhi or Listeria monocytogenes can also lead to sepsis.
Many patients with septicemia or suspected septicemia exhibit a rapid decline over a 24-48 hour period. It has been reported that patients with septic shock require adapted treatment in less than 6 hours in order to benefit from antimicrobial therapy. Thus, rapid and reliable diagnostic and treatment methods are essential for effective patient care. Unfortunately, a confirmed diagnosis as to the type of infection, e.g., sepsis, traditionally requires microbiological analysis involving inoculation of blood cultures, incubation for 18-24 hours, plating the causative microorganism on solid media, another incubation period, and final identification 1-2 days later. Even with immediate and aggressive treatment, some patients can develop multiple organ dysfunction syndrome and eventually death. Hence, there remains a strong need for improved techniques for diagnosis and treatment of patients with infectious diseases, blood-borne infections, sepsis, or systemic inflammatory response syndrome. The ability to rapidly detect infectious pathogens in food, water, and/or environmental surfaces would also have great value for preventing infections and sepsis in the population.